This invention relates to glass filament forming and more particularly to a method for providing a uniform thermal environment at each of a plurality of orificed filament forming tips on a heated glass fiber forming bushing.
It is well known in the art to produce filaments from various thermoplastic heat softenable materials, and especially glass, by flowing streams of molten material from a plurality of orificed tips provided on the bottom of a heated bushing. In the case of glass, the streams are attenuated, usually by mechanical means, into filaments which are then gathered into strands and processed into a variety of commercial products.
One typical use for such strand is in the formation of glass fabrics. In order that a satisfactory woven fabric be produced, it is imperative that the diameters of each glass strand be consistent in a linear plane. Variations in the diameters of glass strands along the length thereof results in a fabric which will not lie flat but rather becomes "puckered". Such a fabric is unacceptable.
Attempts have been made in the past to provide a uniform thermal environment at the bushing tips in order to produce a uniform glass strand. In U.S. Pat. No. 3,068,699 a heat radiating strip was molded to the bushing bottom and extended around the tips. However, there is no external control over the environment that is created.
In U.S. Pat. No. 3,672,857 it is suggested to control the environment around the bushing tips by adding an additional heat fence adjacent to or directly connected to the front bushing tips,thus providing additional heat to the tips.
Another suggested solution (U.S. Pat. No. 3,607,164) has been to plug up the boundary tips such that all active tips are surrounded by similar patterns of heat radiating tips. This would, however, decrease the number of filaments a given bushing could produce, and, as the need for larger bushings have increasing numbers of tips occurs, such a solution is far less desirable.